The custom Google search of PriusChat (in the upper right corner of the page) will find many old discussions. Gasoline vapor is highly flammable. Not recommended. :welcome: Welcome to PriusChat!
The Prius fuel system has several valves that configure for running or refueling. When you refuel in Ready mode, the valves are not properly configured. That said, many people do it and get away with it, but I don't recommend it for this and other reasons. Tom
OOPS! Based on Bill's post, I guess I'm one of the lucky ones. I've filled my tank twice while in READY mode because I didn't want to go through the startup sequence of the engine running until it gets back into Stage 4. I've not noticed any problems after doing this twice - I guess I'm lucky. The engine was well warmed-up and in Stage 4 when I filled up both times.
Not recommended, but if the ICE is not running at Ready Mode during fill-up you MAY get away with it.
Better and safer to turn it off. Just how much do you think it is going to cool off in the 5 minutes it takes to get gas and be on your way?
Like I said, I have done it in Ready mode once on accident. Interesting link, I have actually seen this memorial at school, University of California, San Diego student George Winne Jr., protesting the Vietnam War, self-immolated on May 10, 1970 at the university's Revelle Plaza before dying the next day.
Just to add to Tom's answer, the car expects you to turn it off before refueling, and sets the vent valve(s) to the proper configuration to avoid damage to the Evap system. Self-immolation is probably a very remote possibility, although it would be quite spectacular.
With the car completely off, worst case scenario: I spend two extra seconds turning it back on. With the car on, worst case scenario: the car goes boom. I don't pretend to speak for everybody, but personally I know which one I would rather happen.
Just for the sake of clarity, then, would you agree there are three distinctly separate reasons for turning the Prius off (or other than "Ready") when refueling? The three being: The fueling system expects the Prius NOT to be in Ready mode when refueling, you could cause damage, similar to over-filling, by having the carbon adsorb the fuel vapors. Presumably, you will use up the carbon prematurely by doing this. There is a safety factor involved in that the Prius could decide to turn on the ICE or a fan and the electrical impulse could produce some spark that, possibly, could ignite the gasoline vapors. It is illegal in some states (Illinois is one) to fill an automobile while it is running. (There is some question whether this applies if the ICE is off, but the intent seems clear.) I don't know that the safety factor in 2. is truly an issue. I think it is much more likely that a fire or explosion will result from making a call on a cell phone while you are holding the gas pump than having such an accident result from having an electric switch in the Prius turn on or off. If you are in a place where 3. doesn't apply, then I think the real question is whether the value of leaving the car in Ready mode exceeds the danger of damage to the fueling system from filling without leaving Ready mode. Thoughts? Comments?
Actually, its ok for the carbon canister to adsorb the fuel vapor (that's what its for) but you don't want to saturate it with liquid fuel. And you don't want to get liquid into the area between the bladder and the metal outer tank. But I do agree with the three separate reasons.
Ordinarily, I would never do this. Earlier this week, however, I did fill my Prius while the car was on. My reason is that the 12V battery had died (due to leaving the back-seat light on for a couple days) and I had just jump-started the car. I did not want to risk being stuck at the filling station since the battery had only been recharging for about 5 minutes at that point. I believe that with all modern cars, there is no risk of igniting fuel vapors while refueling with the car running. The risk lies with older vehicles. Under most circumstances, I think it is a good opportunity to save some gas and reduce pollution, so why leave the car running?